Cover Shmover: Judge an Old Book by Its Odor

Take an antique leather-bound book, open it up, and inhale deeply. There’s just something about that old-book smell. And thanks to a new analytical chemistry technique, the volatile organic compounds that compose the aroma could help preservationists keep their collections safe from old-age damage.

Just sniffing an old book can tell chemists a lot about the state of the paper in a vintage volume, including its level of acidity, lignin and rosin, which are all important variables for deciding how to approach preserving the text.

“During my research work, I noticed that conservators would often smell paper as if they could tell whether certain degraded papers smell differently to others,” said Matija Strlic, a chemist at University College London, and lead author of a new paper in Analytical Chemistry. “Being a chemist, I thought, if that’s what they do, perhaps there is a scientific way of sniffing out the degraded paper.”

“The aroma of an old book is familiar to every user of a traditional library. A combination of grassy notes with a tang of acids and a hint of vanilla over an underlying mustiness, this unmistakable smell is as much part of the book as its contents. It is a result of the several hundred identified volatile and semivolatile organic compounds (VOCs) off-gassing from paper and the object in general.”
—Matija Strlic, et al, in Analytical Chemistry

The solution he developed is called “material degradomics.” It relies on identifying the set of compounds associated with degrading paper, using chromatography and spectroscopy. Using a benchmark set of papers of varying ages that have been well-characterized, the researchers were able to associate different smells with different papers in varying states of preservation. Eleven smell components were correlated with important paper qualities.

Though Strlic noted that this first journal article was just a proof of concept, once the details are worked out, he thinks the technique could be used on site at the world’s archives and museums.

“I can imagine that in the future, one might have even a handheld instrument to sniff objects and try to tell which ones are more or less degraded,” he said.

How could knowing the paper’s profile help preservationists? Paper produced until about 1850 was made to last for millenniums. The development of new wood-pulping techniques in the middle of the 19th century and the use of rosin sizing reduced the longevity of paper. The acidity of paper made with these techniques causes them to degrade more quickly than the older papers — or newer ones made with different methods after 1990.

“These papers are particularly unstable,” Strlic said, with lifespans that are measured in only hundreds of years.

Now, paper made in 1850 or so is getting old, and some of it has begun to degrade. It’s become imperative to identify which texts are most vulnerable — and that’s what Strlic’s new technique allows.

Other conservation tests can also tell conservators how badly degraded paper is, but they all destroy at least some of the material they’re trying to preserve.

“All of the tests I know of are destructive, meaning they consume some of the material or one needs to touch the object,” Strlic said. “In some cases, especially if you are dealing with a very valuable object, even touching is something that is not allowed, so conservators very often like to see methods which are entirely noninvasive.”